Project Summary/Abstract An estimated 5.2 million older Americans had Alzheimer's disease in 2016. As the population of the United States ages, the number of dementia cases is projected to reach 13.8 million by 2050, with high costs for the health care system and society. It is critical to identify modifiable behavioral factors that slow (or accelerate) age-related and pathological cognitive decline. Alcohol consumption is one such behavior that has extensive consequences for cognitive functioning. Although alcohol dependence and abuse may lead to structural and functional brain damage, epidemiological studies suggest a possible protective effect of light-to-moderate alcohol consumption in aging populations. Alcohol, however, may not benefit everyone who drinks moderately, especially when individuals reach older ages. In addition to the effect of alcohol on cognition, individual differences in cognitive functioning may predict the level of alcohol consumed. Impaired vs. preserved cognitive performance may be both a consequence and predictor of alcohol use. Yet, this reciprocity is neglected in studies of older adults. Most work has focused either on younger or older samples, or treated age as a confounder. The proposed research is the first systematic attempt to examine the reciprocal, synergistic effect of alcohol consumption and cognition by adopting a developmental aging perspective. The specific aims of this research are (1) to identify the reciprocal, longitudinal association between alcohol consumption and cognition, (2) to examine whether this association varies by age, and (3) to test patterns of alcohol consumption and dependence in older adulthood as risk factors for incident cognitive impairment and dementia. This research will leverage individual participant data (IPD) from four well-established national and international longitudinal cohorts that have at least two repeated measures of alcohol consumption (frequency and quantity) and cognition, spanning from middle adulthood to very old age. The proposed IPD analyses will provide unprecedented insights into the reciprocal relation between alcohol consumption and cognition, and how this bidirectional association changes with advancing age. It will lay the groundwork for future studies on the development of effective interventions targeted at enhancing cognition and promoting healthy aging.